It is known to provide Patterning for Nanoimprint Lithography (NIL) of surfaces, including diamond flat surfaces. A problem with patterning diamond surfaces is that it is very difficult to create complex nano-scaled structures on diamond surfaces, particularly for features such as, any surface pattern more complex than a straight line or mesas or line structures with extreme surface smoothness. It is especially problematic for nano-structures that require the characteristics of smooth vertical side walls, and a high height to width aspect ratio.
Typically to provide conventional patterning of diamond surface a process called direct Focused Ion Beam (FIB) is used, usually of the order pico or micro amps over an area of 100 nm2. A number of papers disclose a process for diamond patterning for subsequent use in NIL. For example, a paper published by Taniguchi J., Tokano Y., Miyamoto I., Komuro M., Hiroshima H., “Diamond Nanoimprint Lithography”, Nanotechnology 13, page 592 (2002) discloses how to successfully pattern diamond structures for the purposes of nanoimprint lithography. The process disclosed involves exposing the diamond surface coated in an electron beam resist to a lithographic pattern generated by an electron beam. The resist is then developed and the exposed diamond is subjected to an oxygen Reactive Ion Etch (RIE) which subsequently forms the patterned diamond mould. Typical pattern sizes are of the order of 2.0 μm can be produced on a diamond surface.
Another paper by Ando Y., Nishibayashi Y., Furuta H., Kobashi K., Hirao T., Oura K., “Spiky Diamond field Emitters”, Diamond and Related Materials 12, page 1681 (2003) used a similar method to produce diamond field emitter tips. Rather than using a resist as a masking agent, aluminium spots were deposited onto the surface via conventional photo lithography. With this technique approximate 1.5 μm spots in size can be successfully applied to the surface. Another masking method discloses depositing metal on a diamond substrate to form a mask and subsequent Reaction Ion Etching (RIE) using an oxygen plasma, see for example disclosure in JP63220524. It has been found that it can be technically very difficult to deposit metal in the nano-scale. Such a deposition also requires a number of steps that are technically very complex to perform and achieve complex structures with dimensions in the nano-scale.
Stanishevsky A., “Focussed ion beam patterning of diamond like carbon films” Diamond and related Materials 8 page 1246 (1999) demonstrates patterning of diamond like carbon films by allowing a Ga+ ion beam to sputter material that is exposed to the beam. When removing material across a large surface area, such sputtering has the disadvantage of being very time consuming relative to plasma etching. When milling to obtain elevated features uses a positive exposure (which is usually a larger area) which requires that far more material be removed.
Böttcher A., Heil M., Stürzl N., Jester S. S., Malik S., Pérez-Willard F., Brenner P., Gerthsen D., Kappes M. M., “Nanostructuring the graphite basal plane by focused ion beam patterning and oxygen etching”, Nanotechnology 17 p5889 (2006) uses the combination of Ga+ ion beam patterning and oxygen etching to obtain a patterned structure on a graphite surface. The function of the Ga+ ion beam is simply to increase the graphite surface susceptibility to the oxygen plasma etch where the beam strikes. A number of problems exist with this process. The oxygen etching is in the form of a high temperature (500° C.-700° C.) reaction with oxygen gas. The process utilises a positive exposure to the graphite rather than a negative exposure, thus the oxygen etch merely enhances the ion milling effect.
Nano-imprinting with Patterned Diamond potentially has many applications, for example in the microelectronics industry. There is a need in the microelectronics industries to provide a highly re-producible, low cost method for producing circuits, nanowires or transistors. The use of patterned diamond NIL stamps to form etch masks in resist layers for microelectronic circuit construction by lithographic processing is one way to address this problem.
The imprinting of micro- and nano-scaled patterns over large areas to produce high thermal conductivity interfaces is desirable in the industry, similar to that described by Brunschwiler et al. (2005)—Brunschwiler T., Kloter U., Linderman R., Rothuizen H., Michel B., “Hierarchically Nested Channels for Fast Squeezing Interfaces with Reduced Thermal Resistance”, 21st IEEE SEMI-THERM Symposium (2005). The generation of these interfaces is of particular interest to the microelectronics industry as the chip/transistor power density is currently being restricted by the rate of heat transfer across such interfaces.
European Patent Publication Number EP 0 400 791 describes a method specifically to fabricate “device functional materials” or “circuitry of interconnected devices” using two sequential processes. The first process uses irradiation, using accelerated ions, to create a surface modification, normally resulting in the removal of a masking layer, (i.e. of “a surface free of a masking layer greater than 100 nm”). Followed by a second process, uniform irradiation which selectively modifies areas exposed by the first process which results in a surface modification. This European patent requires a “masking layer” in which the “surface modification” is the local removal of this masking layer aided by the focussed ion beam exposure. The absence of this layer allows the selective modification which is etching material from the exposed areas where it is not protected by a mask.
A paper published by Wang et al in American Institute of Physics, Melville N.Y. Vol. 56, no. 8, 19 Feb. 1990, pages 749-751 describes a positive masking process, not dissimilar from that described in EP 0 4 00 791. Japanese patent publication number JP 63 281488 describes a process, very similar that described in EP 0 400 791 and Wang, whereby convergent beam of ions are used to create an amorphous layer over the area the beam is scanned. This amorphous layer is then selectively etched. In the example given the pattern is applied to a GaAs substrate, using a Si ion beam at 200 kV and the etch is wet using HCl above ambient temperature. The application is specifically to create line structures for a diffraction grating.
Another publication by NTIS TECH NOTES, US Department of Commerce, Springfield, Va., US, 1 Aug. 1988, page 640, 01/02 describes a process to create a mask to photochemical etching from the surface of a semiconducting substrate by changing the local electrical properties of the substrate via ion implantation. The etch is specifically using a gas with a “low concentration of a highly reactive gas”. In the specific description given, Cl is the reactive gas where photochemical etching is induced by a laser which is applied to a GaAs substrate.
European Patent Publication No. EP 0 321 144 describes both positive and negative patterning to create semiconductor devices from multi-layer structures. The description makes reference to at least one layer being a pre-deposited mask which is essential. In examples given, the ion beam patterning referred provides a means of removing a layer below this first masking layer, not as a modification of the surface.
Another paper, Rennon et al, published in Microelectronic Engineering, Elsevier Publishers BV, Amsterdam, NL, vol. 57-58, pages 891-896, 2001 describes a method for patterning InP via the creation of a positive mask from the InP due to the implantation of Ga ions accelerated at 100 kV into the sample. It also requires a hot HF wet etch is required. Another paper published by Brugger et al in Microelectronic Engineering, Elsevier Publishers BV, Amsterdam, NL, vol. 35, pages 401-404, 1997 describes a positive masking process, where a Ga ion beam creates a mask/selective (wet) etch from KOH when applied to Si.
PCT patent publication number WO03/056611 describes a resistless method to create a semiconducting mask by doping a carrier material with an ion beam implantation then exposing it to a wet chemical etch to remove the undoped material. The process relies on a semiconducting layer to act as a hard mask, which its self can be the carrier layer. The ion beam effect relies on the doping of this semiconducting layer.
U.S. Pat. No. 5,580,419 describes a system to create integrated circuits using an ion beam. This system includes the steps: vacuum system and mounting system to transport wafers between chambers, and an ion beam to carry out the processes of FIB etching, Gas assisted ion beam etching and ion doping.
U.S. Pat. No. 4,622,918 discloses a processing chamber and means of transporting wafers between different process which can be applied within the single high vacuum chamber.
US patent Publication Number US2008/038926 discloses a treatment to an existing masking layer to enhance feature properties after subsequent etching. It creates part of a process of patterning a thin film which is coated by a masking layer (presumably pre-patterned by traditional resist based techniques). The enhanced masking layer protects the substrate from etching via an electron beam assisted plasma, primarily comprising of CxHy gasses. The context of the process is semiconductor/microelectronic processing.
It will be appreciated that many of the citations above are applicable to the semiconductor industry and producing integrated electronic circuits only and are not related to carbon based or otherwise hard surfaces. Other applications of patterning surfaces that suffer from the above mentioned problems and required complex processes to manufacture include:                Microelectromechanical systems (MEMS),        Photonics e.g. waveguides, or other microelectronics e.g. similar to those described by Ando Y., Nishibayashi Y., Furuta H., Kobashi K., Hirao T., Oura K., “Spiky Diamond field Emitters”, Diamond and Related Materials 12 page 1681 (2003).        Precious gemstone/diamond marking, for example as described in U.S. Pat. No. 6,391,215 by James Gordon Charters Smith et al. (2002).        
Heretofore, no process had been proposed to produce sharp, precise and high aspect ratio three dimensional scaled patterns on a carbon-based surface, for example a diamond surface, using a simple process to overcome the above mentioned problems.